use case: high precision trail mapping

[icycle]

Hi,
I've been on the hunt for the "most accurate" iPhone GPS app for
purposes of creating highly accurate trail maps for a network of
trails I create/maintain. By this I mean the GPS track length comes
closest to the trail length as measured by a mountain bike (wheel
rotation count) computer, and shows the trail's twists and turns that
most apps miss in their quest to smooth out the track.

I've been going around in circles on external GPS's and still seeing
inaccurate tracks, etc. (see http://forums.mtbr.com/9050131-post1.html
if interested) I finally settled on the Magellan ToughCase add-on for
my iPhone 3GS.

I have read excellent reviews about both Gaia and GPS Kit (see review
here which favors Gaia: http://dl.dropbox.com/u/15393086/BPL/iPhoneGPSapps.htm)

Regarding accuracy, I see several previous conversations in this group
about GPS sampling rate:
http://groups.google.com/group/gaia-gps/browse_thread/thread/53056602f3ada12f/eae25a1516dd5ebd
http://groups.google.com/group/gaia-gps/browse_thread/thread/b0291b42b93c44b0/97237a5f03ed1e84
both of which seem to indicate that Gaia is no longer capturing all
data points, but rather is doing adaptive capture to preserve
battery. Is this still true and is there any supported way to get all
the data for this use case where it truly is desirable over the impact
to battery life?

Thank you,
Brett

[Bill Burge]

If you're using the Magellan add on gps, the accuracy in question is related to Magellan, and not the iPhone or GaiaGPS.

Bill Burge
Typoed on my iPhone...

[Gaia GPS Support]

Hi Brett,

I'm sorry, Gaia GPS does not currently have a setting where we collect all data points.  We currently use the Ramer-Douglas-Peucker algorithm to choose data points and use them to make a track.  I love hearing from users about the ways they use or want to use Gaia GPS and I appreciate your feedback.  If you have a moment, please contribute your idea of adding a setting to Gaia GPS that allows users to collect all data points to our UserVoice page.  If you add your idea to our UserVoice page, other users can comment on the idea or vote for it to be developed.  If we decide to develop the idea or release it, we can easily update all users interested in the idea from our Uservoice page.

Thank you so much for your feedback.  Please let me know if you have any other questions or comments about Gaia GPS. 

Regards,

Savannah

Savannah Henderson
User Support
www.GaiaGPS.com
415 335 7447

[icycle]

On Mar 20, 1:26 pm, Bill Burge <4foo...@gmail.com> wrote:
> If you're using the Magellan add on gps, the accuracy in question is related to Magellan, and not the iPhone or GaiaGPS.

For accuracy of GPS signal, yes, I agree. But I was referring to
accuracy of the track as compared to reality. Sorry about the
confusing double usage.

-Brett

[4Footed]

You should abandon the iphone as the platform of choice if that level of accuracy is required.

Switch to a dedicated GPS. For important stuff, I use a Garmin Oregon 450t.

When configuring tracks, you can customize the interval: Distance or Time

For distance, the default is 0.06 miles. While I have not tested it, I was allowed to set the interval to 0.01 miles.
For time, the default is 30 secs, but 1 sec was accepted.

You would then want to set Auto Archive to "When Full".

I wasn't confused, except by your choice of the iPhone for something where you want better-than-consumer grade accuracy.

Bill Burge

[icycle]

On Mar 20, 1:29 pm, Gaia GPS Support <supp...@gaiagps.com> wrote:
> I'm sorry, Gaia GPS does not currently have a setting where we collect all
> data points.  We currently use the

> Ramer-Douglas-Peucker<http://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_al...>

> algorithm
> to choose data points and use them to make a track.

That's too bad, I was really hoping there was a way. I still have
some hope remaining with GPS Kit.

> If you have a moment, please contribute your idea of adding a
> setting to Gaia GPS that allows users to collect all data points to
> our UserVoice page

I created a new idea based on this discussion:
http://gaiagps.uservoice.com/forums/118985-general/suggestions/2699650-allow-for-high-max-gps-sample-update-frequency-rat

Thanks,
Brett

[Gaia GPS Support]

Thanks for adding your idea to our UserVoice page, Brett. We really appreciate your feedback and we will let you know if we decide to develop your suggested feature.

Regards,

Savannah

Savannah Henderson
User Support
www.GaiaGPS.com
415 335 7447

[Anna Johnson]

We apply the filtering to the tracks with a tolerance of 0.000005
degrees, which is under a meter at 45 degrees of latitude, well within
the accuracy of the GPS. The filtering helps a lot to keep tracks
manageable when the user stops for awhile in the same place, and
simplifies tracks when they're mostly going straight.

I don't think that the iPhone app is appropriately suited to your
purpose, but I don't think the filtering detracts from the track
accuracy in any meaningful way.

-Anna

--
Anna Johnson
GaiaGPS.com
415-335-7447

[icycle]

On Mar 20, 2:23 pm, 4Footed <4foo...@gmail.com> wrote:
> You should abandon the iphone as the platform of choice if that level of accuracy is required.

I did a lot of background research on this before deciding to go this
route; here's why I made this choice. I'm only using the iPhone as a
mobile computing platform in this regard. I have added on an external
GPS using a slightly dated but still very capable SiRFStar III chipset
and proper GPS antenna, so GPS hardware wise I'm on ~equal footing.
The iPhone app store hosts hundreds of GPS apps, but sadly most of
them discard data points acquired, most likely because the iPhone's
built in GPS is noisy (poor chipset and antenna). However, consider
this app on the iPhone: http://gps-laptimer.de/ This app allows (with
compatible GPS chipsets) direct NMEA protocol access to the GPS data
and thus supports data acquisition rates up to 10Hz. Clearly this far
exceeds common consumer grade GPS handhelds. All the rest of the apps
use the iOS Core Location service which maxes out at ~1.4Hz, which
would be still be plenty for me if only apps would store (and not
discard) this data.

The point is, the iphone is just a platform and given the right HW and
SW, I think it can do as much or more than any handheld. Of course
there are downsides, and I considered them. Battery life, cold
weather performance, touch screen (also an upside, depending on the
day), and durability/waterproofing. Of those, the ToughCase addresses
battery, durability, and waterproofing in addition to the solid GPS
HW.

> Switch to a dedicated GPS.  For important stuff, I use a Garmin Oregon 450t.
>
> When configuring tracks, you can customize the interval:  Distance or Time
>
> For distance,  the default is 0.06 miles.  While I have not tested it, I was allowed to set the interval to 0.01 miles.
> For time, the default is 30 secs, but 1 sec was accepted.
>
> You would then want to set Auto Archive to "When Full".

Thanks for the settings. At this point I'm still hopeful I can make
the iphone route work, but there are many out there that share your
sentiment. I'm just frugal and would like to avoid hundreds+ of
dollars on a device that does one thing when I have this platform
capable of doing what I need just given the right app.

I just read Anna's comments. Thank you Anna for weighing in here. I
had assumed there was a more liberal discard policy (some apps are
doing samples every 10 meters or 2-10 seconds, for example, which
leaves choppy tracks on windy trails. Perhaps I will check out Gaia
after all.

Thanks,
Brett

[4Footed]

Yes, the iPhone is just a platform.

But there's the problem - it is a CLOSED platform; Apple approves all apps before availability.

So, unless you find that something like LapTimer meets your needs, you probably need to Jailbreak and grab a compiler...

Since you don't seem adverse to "nailing two things together" and you are willing to use "consumer grade gps's" like Magellan (I only have Garmin's and IOS devices to play with) you could (my Garmin supports this) use WAAS and raw NMEA out a USB or serial port to a terminal device like a palmtop/netbook/etc that just records the data for later.

http://www.gpsinformation.org/dale/interface.htm

For this level of accuracy, except as a "mental personal abuse project", I would think you would rent something dedicated to this task:

http://www.geodatasys.com/gps.htm (formally Magellan ;-)
from someplace like
http://www.trs-environmental.com/Manufacturer/Trimble.aspx
http://www.waypointtech.com/GPS-Mapping-System-Rentals-c107.html
http://www.monsenengineering.com/Rental%20Equipment.htm

From the sound of your project, you might be able to contact Garmin, Geodata, etc and explain your project and offer to write a nice whitepaper/success story about your project and they might _lend_ you the gear required.

Bill Burge

[icycle]

Bill,
Thanks for the detailed followup. You make a great point about
renting/borrowing commercial GPS equipment. I am mapping a Boy Scout
camp as a volunteer effort for a non-profit, so that plays nicely into
the borrow category. The links were eye opening--I'd heard about
accurate GPS tech, but cm accuracy is amazing.

I did end up buying both Gaia GPS and GPS Kit apps and will see how
they play in the field soon. It'll likely be good enough for the
level of detail I need. My biggest concern was having a 1 mile curvy
trail represented by a 0.6 mile GPS track, which is what's happening
today.

I'll still be on the lookout for other post processing GIS software to
make nice maps. Today I'm using Earth, which functionally isn't bad,
but the end result isn't much to look at.

Thanks all,
Brett

[4Footed]

"...mapping a Boy Scout camp..."

Really? They will eat this up! My boy was a Scout.

Explain: "it's not just to help the boys and scout masters and to inform the parents of the options for recreation and the safety of their boys, provide accurate data for safety purposes or 'heaven forbid, first responders...'; but also to satisfy requests for data from local government agencies and insurers."

Man! If you're close enough to the provider, you might be able to get them to lend you someONE to help you with it!

Good luck!
Bill